Without honeybees, wild bees may still provide full pollination service on cultivated pumpkins

Recent declines in managed and feral honey bee populations have greatly increased interest in the current and potential role of wild pollinators in agricultural pollination. Pumpkin and other Cucurbita spp. crops have great potential to be served by wild pollinators in the United States and Canada because of a reliable and widespread group of bee species that are commonly associated with their flowers, including bumble bees (Bombus spp.) and squash bees (Peponapis spp. and Xenoglossa spp.). We examined the density of wild pollinators on 20 farms in Virginia and Maryland (USA) during the summer of 2006 in order to assess the potential of wild pollinators to contribute full pollination in the absence of honey bees. We examined nest site preference (within or outside of crop areas) of squash bees at one farm and one controlled environment (a large screen house with several nesting blocks) and also analyzed squash bee densities in regard to tillage and irrigation practices. We found squash bees to nest preferentially within crop areas and near the vines and leaves of their host plant. Although squash bees typically place some of their brood cells within tillage depth, we did not find that squash bee densities on no-till farms were greater than on till farms. We did find, however, that squash bee densities were greater on farms with irrigation. Using published data on pollinator abundance and fruit production in Cucurbita crops, we found that wild bee densities were sufficient to contribute full pollination on 17-19 of the 20 pumpkin farms studied. This study joins a similar study on watermelon pollination in California in showing that wild, unmanaged pollinators can, in some circumstances, contribute full pollination on crops usually managed for honey bee pollination.